Removal of particulate matter from fluids has received considerable attention in many technical areas. For example, efforts continue in the automotive industry to improve filtration for the removal of particulate matter from oil and gasoline. In the manufacturing of integrated circuits, the presence of particulate matter in processing fluids can result in defective parts. Accordingly, considerable attention has been focused on effective ways of removing any particulate matter which can precipitate on substrates such as printed circuit boards. Perhaps most significantly is the effort being made in the health care industry to screen/purify blood and other fluids which are injected into the body for possible contamination with viruses, such as Human Immunodeficiency Virus (HIV) and hepatitis, bacteria, fungi and parasites.
Particulate matter has been removed from fluids by several methods. One such method employs traditional mechanical pass through filters having preselected pore sizes to screen out particulate matter. The pore size of the filter will vary directly with the size of the particulate matter to be removed from the fluid. Such filters, however, are disadvantageous because they are non-specific as to the type of particulate matter which is removed. Once a pore size has been selected, the filter will pass all particulate matter, including both contaminants and non-contaminants, having a particle size less than the selected pore size.
Separation of particulate matter within a fluid has been established with an electrical field using field flow fractionation. Like centrifugation, field flow fractionation is an elution technique. This procedure employs the use of density differentials (e.g. sedimentation), thermal gradients and transverse electrical fields to name a few.
Each of these methods has disadvantages for use in the purification of fluids, such as in the treatment of blood plasma for the removal of harmful substances such as viruses, bacteria, fungi and parasites. In field flow fractionation techniques utilizing a transverse electrical field, the hydrodynamics of the fluid allows precipitation of larger protein particles simultaneously with the extraction of substances which are responsive to the imposed electrical field. The removal of protein particles with the desired substances adversely affects the effectiveness of the separation process and also modifies the product (e.g. blood plasma) itself.
Another separation method employs an ion-exchange column which separates materials based on their differential binding to charged surfaces in the presence of an electric current. Ion-exchange columns, however, become quickly saturated as the materials precipitate out on the electrode and therefore require frequent cleaning.
Any process including field flow fractionation, ion-exchange columns, and the like which utilizes a current flow in a conductive fluid will produce a gaseous byproduct which may remain suspended in the fluid body. With blood plasma suspended gaseous byproducts may lead to formation of an embolism within the human body.
Electrostatic devices have been proposed for removing particulate matter from dielectric or non-conductive fluids, such as petroleum products as disclosed, for example, in Van Vroonhoven, U.S. Pat. No. 3,484,362 and Watson et al., U.S. Pat. No. 4,372,837. Such electrostatic filters generally include a chamber for receiving the fluid, an electrostatic field generating assembly for generating an electrostatic field across the flowing fluid and a dielectric material within the chamber.
Such devices, while effective for removing particulate matter from non-conductive fluids are ineffective for removing particulate matter from a conductive fluid. Conductive fluids cause shorting due to the low electrical resistivity of the fluid between electrodes, thereby preventing an effective electrostatic field from forming.
It would therefore be a significant advance in the art of separating substances from a conductive fluid, to provide a device and method which can effectively perform the separation in a time and cost effective manner. A further advantage would be obtained if selective separation can be accomplished without removing desirable non-contaminants from the fluid.